GCSE AQA C1 Notes

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Atomic Structure

Atoms are very, very small particles made of subatomic particles: protons, neutrons and electrons. Protons are positive, neutrons neutral and electrons negative. Atoms have shells/energy levels around them which have electrons on them. The number of protons in an atoms identifies the element.

Smaller number on a periodic table element is the proton/atomic number, the larger number is atomic mass/mass number. Atomic number is the number of protons/electrons and the atomic mass is the sum of protons and neutrons.

In any stable atom, the number of protons equals the same number of electrons.

In the first shell, the maximum amount of electrons in two. After that the maximum is eight.

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Ionic Bonding

Ions can either be positive or negative.

Ionic bonding can only happen between a metal (provides positive charge) and non-metal (provides negative charge).

Ionic bonding involves the movement of electrons from one element to another.

An atom is most stable when it has a full outer shell.

When an atom is bonded ionically, it'll change charge. If the number of electrons is decreased, its charge is increased because the number of protons outweigh that of the electrons. If the number of electrons is increased, the charge is decreased because the number of electrons outweigh that of the protons.

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Covalent Bonding

Covalent bonding only happens between a non-metal and another non-metal.

It involves the sharing of electrons.

Can produce simple molecular compounds (Like oxygen) or giant covalent structures (Like diamond).

Examples:

Chlorine gas

Carbon dioxide

Covalent bonds are very strong and difficult to break.

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Balancing Chemical Equations

In order to balance an equation, the number of atoms on each side of the equation must be equal. We can do this by adding numbers in front of an atom's symbol, though we cannot change the smaller number.

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Limestone and Building Materials

Limestone is a building material which, chemically, is calcium carbonate. It is strong and easily carved into a desired shape.

When you mix limestone with clay and heat it, you get cement.

When you mix cement and sand, you get mortar.

If you mix mortar and small stone, you get concrete.

Limestone is mined from quarries. Quarries can be an annoyance since the machinery used there produces a lot of noise, dust and pollution. Quarries also take up a lot of land and ruin the landscape. However, limestone is a very valuable material and they provide jobs.

The limestone cycle starts with calcium carbonate (Limestone, CaCO3), it can then be heated (thermal decomposition) to produce calcium oxide (CaO) and carbon dioxide (CO2) (calcium oxide is alkaline and can be used to neutralise acidic soil), water can then be added to calcium oxide to produce solid calcium hydroxide (Ca(OH)2), you can then add more water to solid calcium hydroxide to produce a calcium hydroxide solution (Ca(OH)2(aq)) and finally the calcium hydroxide solution can be turned back to limestone through adding carbon dioxide (By blowing into it and it goes cloudy).

Thermal decomposition can happen to other carbonates, as well (Copper carbonate, copper carbonate, zinc carbonate and magnesium carbonate).

Carbonates at the top of group 1 are more difficult to decompose (E.g. potassium carbonate)

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Extracting Metals

A lot of things are made of metal, and so it is important to get the metals needed for making those things.

An ore is a type of rock that has the metal of interest in it in abundance, the metal is often chemically combined with another element plus impurities.

Ore can then be concentrated and then chemically reacted to be purified to the pure metal.

Though extracting and purifying some ore is expensive, it is overall economically viable because the metal produced can be sold for a lot more.

Metals less reactive than carbon can be extracted through displacement. If a metal is more reactive than carbon, it can be extracted by melting the ore and using electricity (Electrolysis) (More expensive because it uses a lot of energy).

Gold can be found pure/native (Not in an ore).

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Fractional Distillation of Crude Oil

Crude oil is always found deep in rock, usually under the ocean, and can be extracted by drilling with oil rigs.

Crude oil is a mixture (Not chemically joined) of many different compounds. It can be easily separated.

3 liquids in a compound, every compound has its own boiling point (The point at which liquid turns into a gas). This means that we can separate all the compounds through evaporating each one of them at their different boiling points, this is called distillation.

Crude oil compounds with lower boiling points are highly flammable and has a low viscosity. Compounds with a longer chain and have higher boiling points are less flammable and have high viscosity. These chains are called hydrocarbon molecules.

In distillation, the tower is made to be cooler at the top and warmer at the bottom. Compounds with different boiling points evaporate at different temperatures and are then removed from the tower as the pure compound.

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Cracking Hydrocarbons

Shorter chain hydrocarbons are more useful, longer chains are less useful.

However, longer hydrocarbon chains can be separated into smaller chains through a process called cracking.

Cracking involves heating heat-proof wool soaked in the long-chain hydrocarbon and a ceramic catalyst in a glass tube which then produces a gas collected in another test tube upside down in water. This reaction is a form of thermal decomposition.

Alkenes have double-bonds, alkanes don't.

Alkenes, like alkanes, have a general formula of CnH2n.

Alkenes are unsaturated because they have less hydrogen atoms.

A test for unsaturated hydrocarbons involves a reaction with bromine water, if the bromine changes colour then an unsaturated hydrocarbon is present.

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Polymers

Ethene is an alkene, a gas and is very flammable. The smaller molecules can be joined together to form a longer chain through a process called polymerisation. The plastic this process on ethene creates is called polyethene.

Polymerisation involves breaking apart the double bond in a monomer and creating a polymer by connecting it to other molecules.

You must draw molecules in a molecule in brackets and put a small n next to the bracket.

Polymers are often thrown away and they don't naturally decompose, leading to landfills filled with plastics for many, many years. To combat this, biodegradable polymers are being developed by adding a substance called cornstarch. We can also recycle discarded polymers.

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Ethanol

Ethanol is used in alcoholic drinks, disinfectants, perfumes, aftershaves and fuel.

The first way of creating ethanol is by fermentation and the second is by reacting ethene and steam.

Fermentation:

Needs sugars

Needs yeast

Needs water

All these combine together to form ethanol and carbon dioxide

Much cheaper

Low temperatures

Produces CO2

Lots of land for the crops that produce the sugar

Reacting ethene with steam:

Ethene and steam are reacted together with a catalyst at high temperatures to create ethanol.

Ethene + Water -> Water

Hydration

No CO2 produced

Quicker

Requires less people

Expensive

Using crude oil (Non renewable)

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Emulsions

Without an emulsifier, water and oil with not mix.

By adding an emulsifier, they will mix together.

Droplets of oil stay as droplets.

Emulsions:

More viscous

Better at coating

Better texture

Look better

Things you may eat: salad dressings, mayonnaise, ice cream, milk.

Paints

Cosmetics

Egg yolk is an effective emulsifier.

Inside the emulsifier, there are very small molecules with a hydrophilic head and a hydrophobic tail. The hydrophilic head sticks to the water and the hydrophobic tail sticks to the water droplets, making the water and oil ultimately stick together and not separate.

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Saturated and unsaturated fats

Saturated fats:

Solid at room temperature

Higher melting point

From animals (Lard, butter)

Less healthy

No double bonds in the carbon bonds

Unsaturated fats (Oils):

Liquid at room temperature

Lower melting point

From plaints (olive oil...)

More healthy

Has double bonds

When reacted with bromine water, if there is a colour change, unsaturated fats are present. If the colour doesn't change, saturated fats are present.

If you react an unsaturated fat with hydrogen gas using a nickel catalyst at 60 degrees celsius, it can be converted into saturated fat.

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Earth Structure and Plate Tectonics

The Earth's atmosphere is a layer of gases 10km around the Earth's crust. The Earth's crust is made up of several 'jigsaw puzzle pieces' called tectonic plates.

The thinnest layer of the Earth is the crust, then the thicker mantle and the core: inner and outer.

Alfred Wegener proposed a theory in 1915 known as continental drift. This theory involved the idea that continents were once part of a larger land mass in the past.

In the core of the Earth, there are radioactive processes that produce heat. The mantle is heated by the core and causes the mantle to move around in a convection current. These convection currents move tectonic plates.

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Earth's Atmosphere

The Earth was first formed around 4.5 billion years ago, it was a big hot ball of rock with no atmosphere or tectonic plates; there was a lot of intense volcanic activity which emitted a lot of gases (Carbon dioxide, water vapour, methane and ammonia). Once the Earth cooled down, the water condensed into oceans and a lot of the CO2 dissolved into the water.

Around 3.5 billion years ago, the first signs of life happened, these very simple lifeforms performed photosynthesis which took in CO2 and produced oxygen. All these small photosynthesising cells contributed to the beginnings of the Earth's atmosphere by creating a lot of oxygen.

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Earth's Atmosphere and Miller-Urey

The Primordial Soup theory:

Two scientists used apparatus and the same chemicals that'd be in Earth's early atmosphere to try and recreate the beginnings of life

They were successful in creating organic chemicals such as amino acids and the buildings blocks of life

How exactly life occurred is still unknown

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Fractional Distillation of Air

Air is a mixture of gases. The largest component of air is nitrogen (78%), then oxygen (21%) and other gases (1%).

Air is separated in a similar to way in crude oil but in reverse by cooling the air to make all the separate gases in liquid form. By warming it slightly, the liquids when start to evaporate at different boiling points.

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Burning Hydrocarbon Fuels

We need to burn hydrocarbon fuels for transport, generating electricity and generating heat.

Certain chemicals when the fuels are burned can be dangerous. Sulphur dioxide and nitrogen oxides can cause acid rain and particulates soot (carbon) can cause global dimming.

When we burn hydrocarbon fuels, both carbon and hydrogen are oxidised, producing carbon dioxide (Which contributes to global warming) and water.

Sometimes when burning hydrocarbon gas, incomplete combustion occurs (Low oxygen) and carbon monoxide, a poisonous gas, is produced.

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Biofuels

Biofuels are produced from plants (Lower energy yield) or from ethanol via fermentation and are more environmentally friendly than hydrocarbon fuels.

Ethanol production:

Sugar canes are used as a raw material for the fermentation of ethanol

Ethanol can then be used to power vehicles

The main benefit to this is that it doesn't produced carbon dioxide and instead the sugar cane plants being grown even take in carbon dioxide and emit oxygen.

Carbon neutral

--

Using biofuels:

Provides jobs

Low tech

Low energy

Cheap

Carbon neutral

Renewable

Shortage of food

Possibility of crop failure

Slow

Habit destruction

Reduction in biodiversity

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The Periodic Table

Groups are vertical columns.

Group 1 elements are called the alkali metals, they are very reactive.

Metal + Oxygen -> Metal oxide

Metal + Water -> Metal hydroxide + Hydrogen

Group 8/0 elements are very unreactive and are known as 'noble gases'.

The group of an element determines the number of electrons in its outer shell.

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